1. Field of the Invention
The present invention relates to a radar system and method, and more particularly, to a system and method for performing adaptive broadcast radar operations.
2. Discussion of the Related Art
Radar systems may be represented by a bistatic or multistatic radar system. A multistatic radar system has many receivers that are separated from one or more transmitters. The radiated signal from a transmitter arrives at a receiver via two separate paths. One path may be a direct path from the transmitter to the receiver, and the other path may be a target path that includes an indirect path from the transmitter to a target to the receiver. Measurements may include a total path length, or transit time, of the target path signal, the angle of arrival of the target path signal and the frequency of the direct and target path signals. A difference in frequency may be detected if the target is in motion according to a doppler effect.
Knowledge of the transmitted signal is desirable at the receiver if information is to be extracted from the target path signal. The transmitted frequency is desired to determine the doppler frequency shift. A time or phase reference also is desired if the total scattered path length is to be determined. The frequency reference may be obtained from the direct signal. The time reference also may be obtained from the direct signal provided the distance between the transmitter and the receiver is known.
Multistatic radar systems may be capable of determining the presence of a target within the coverage of the radar, the location of the target position, and a velocity component, or doppler, relative to the radar. The process of locating the target position may include a measurement of a distance and the angle of arrival. The measurement of distance relative to the receiving site may desire both the angle of arrival at the receiving site and the distance between transmitter and receiver. If the direct signal is available, it may be used as a reference signal to extract the doppler frequency shift.
Known radar systems may transmit a signal beam in a specific direction to search for targets. Once a target has been detected, the beam may be directed to follow the target. The receiver may receive scattered signals reflected off the target. By knowing the transmitter beam parameters, the receiver may perform operations to determine the target parameters, as disclosed above.
Future airborne radar systems may operate in a difficult environment where the detection of small and maneuverable targets may occur against a strong clutter background and jamming operations. Directed beams of energy from transmitters may be susceptible to jamming countermeasures and detection. Power aperture increases may not be effective to overcome these limitations and countermeasures against radar detection. Thus, future systems may desire increase sensitivity without increasing power requirements. This condition may be applicable especially to radar systems where the transmitter power is not controlled by the receiving party.
Mobile radar systems often operate in the presence of jamming interference and monostatic clutter that produced naturally by ground reflections. Difficulties may arise if both the transmitter and receiver are in motion, such as an airborne radar systems. When both the transmitter and receiver of a radar system are in motion, the rank of the clutter covariance may be increased. An increased number of degree of freedom in the receiver system may be needed to achieve a specified level of clutter suppression. Thus a transmitter or receiver in motion may increase the clutter interference with a signal, or increase the complexity within the receiver in accounting for the increased degrees of freedom.